1. Field of the Invention
The present invention relates generally to optical signal switching, and more particularly to a piezoelectric actuated device for switching an optical signal.
2. Description of the Prior Art
Optical data transmission offers many advantages over electrical and broadcast transmission, however, switching optical data from one channel to another has proven to be problematic. Fundamentally, a beam of light is unaffected by passage through an electric or magnetic gradient, thus the usual solid-state methods for switching electric signals are not effective to switch optical signals. Accordingly, various mechanical techniques relying typically on reflection or refraction have been developed to divert optical signals.
FIG. 1 is a schematic diagram of an optical switching array 10 of the prior art. The switching array includes input ports 12 and output ports 14 arranged in columns and rows. To switch an optical signal from the first input port 12 to the output port 14 fourth from the left in the drawing, a diverter 18 located at a point of intersection between the axes of the two ports 12 and 14, diverts the beam from the input port 12 to the output port 14. The diverter 18 can be a mirror, a light pipe, a refractive medium, or the like. Most diverters 18 require a form of actuation to move them into or out of the path of a light beam.
FIG. 2 shows a diverter 20 of the prior art. The diverter 20 is supported within a frame 22 by support members 24, typically arranged in pairs on orthogonal axes as shown. The diverter 20, frame 22, and support members 24 are typically all fabricated from a substrate of silicon. The support members 24 are made sufficiently thin so that the diverter 20 can be rotated within the frame 22 around axes defined by the support members 24. The top surface of diverter 20 is made highly reflective, sometimes by applying a coating, so that light can be reflected with the lowest possible loss of signal strength. FIG. 2 illustrates that as the diverter 20 is rotated simultaneously around both axes as shown, the top surface of the diverter 20 can be made to tilt in the direction 26 indicated. Accordingly, a light beam directed at diverter 20 can be reflected to any of a plurality of output ports 14 by appropriately tilting diverter 20.
FIG. 3 shows a cross-section of the device in FIG. 2 taken along the line indicated. The diverter 30 includes a base 32 suspended within frame 34. The base 32 includes a reflective coating 36. Between the frame 34 and the bottom of the base 32 is an interdigitated electrostatic actuator 37 comprising interdigitated fingers 38 and 39 of the base 32 and frame 34, respectively. The interdigitated electrostatic actuator 37 is actuated by applying electric charges to surfaces of fingers 38 and 39 to cause them to attract or repel. The electric charges can be applied to specific fingers 38 and 39, or to sets of fingers 38 and 39, to modify how much force is applied, and in what direction, to control the induced tilting of base 32.
Diverters 30 suffer several drawbacks, however. In addition to being expensive to produce, they are also sensitive to electrostatic discharges (ESD) and microcontamination. It will be readily appreciated that ESD can destroy the interdigitated electrostatic actuator 37 by melting or fusing fingers 38 and 39. Similarly, microcontamination in the form of fine particles or surface films, for example, can mechanically jam the interdigitated electrostatic actuator 37 and prevent it from actuating. Microcontamination can also create an electrical short between fingers 38 and 39, thereby preventing actuation.
A piezoelectric material is one that will develop an electric potential in response to mechanical deformation, and will mechanically deform in response to an applied electric potential. This is commonly known as the piezoelectric effect. Piezoelectric materials are used in a wide variety of applications including transducers, spark generators for butane lighters, and vibration damping.
Piezoelectric materials are typically either ceramic or polymeric. Common ceramic piezoelectric materials include quartz, cadmium sulphide, and titanate compounds such as barium titanate, lead titanate, and lead zirconium titanate (PZT). Common polymeric piezoelectric materials include polyvinylidene fluoride (PVDF), copolymers of vinylidene fluoride and trifluoroethylene (VDF/TrFE), copolymers of vinylidene fluoride and tetrafluoroethylene (VDF/TeFE), and copolymers of vinylidene cyanide and vinyl acetate (VDC/NA).
Accordingly, what is desired is an optical switching device that can redirect a beam of light between multiple ports and that is less susceptible to microcontamination and ESD failures, and that is readily fabricated according to developed microfabrication technologies.
An optical switching component comprises a stator, a rotor pivotally connected to the stator and including a top surface, a first piezoelectric actuator coupled to the stator and the rotor and configured to pivot the rotor relative to the stator when actuated. Embodiments also can further comprise an optically reflective coating formed on the top surface, and a seed layer between the optically reflective coating and the top surface. Other embodiments further comprise additional piezoelectric actuators, such as two actuators connecting opposite ends of the rotor to the stator and configured to cooperatively pivot the rotor relative to the stator. Four actuators can also be employed where two of the four are configured to pivot the rotor relative to the stator around a first axis and the other two are configured to pivot the rotor around a second axis.
The use of piezoelectric actuators to translate the rotor relative to the stator is advantageous in that piezoelectric actuators are less prone to ESD damage than are electrostatic actuators. Further, when a voltage is applied across a piezoelectric material to create a certain strain, a relatively high amount of stress is developed. Thus, piezoelectric actuators are able to develop substantially more force to accelerate the mass of the rotor than can electrostatic actuators acting on diverters of the prior art. Accordingly, piezoelectric actuators can easily overcome the adhesive effects of microcontamination and thereby make the optical switching components of the present invention more tolerant of less clean environments.
Further embodiments of the optical switching component additionally comprise a controller in communication with the piezoelectric actuator. The controller is capable of applying a voltage to the actuator to cause it to expand or contract along an axis in response to an instruction to switch a beam. In so doing, the controller drives the actuator to orient the top surface of the rotor such that an angle of incidence of a emitted beam from a first port is substantially equal to an angle of reflectance of a reflected beam received by a second port. Further embodiments also comprise a detector in communication with the controller and capable of determining a signal strength of the reflected beam at the second port, the controller being capable of using the output of the detector as part of a feed-back loop in order to optimize the signal strength of the reflected beam at the second port.
The present invention also includes an optical switching device comprising an optical switching component, as provided above, and further comprising an emitter port and a receiver port. The emitter port defines a first line within a plane and is fixed proximate to the optical switching component such that the first line intersects the top surface at about a center thereof to define an angle of incidence between the first line and the top surface. Likewise, the receiver port defines a second line within the plane and is fixed proximate to the optical switching component such that the second line intersects the top surface at about the same point as the first line to define an angle of reflectance between the second line and the top surface.
Further embodiments of the optical switching device comprise a plurality of optical switching components of the present invention arranged in an array, a plurality of emitter ports, where each emitter port is associated with one of the plurality of optical switching components, and at least one receiver port associated with each optical switching component. Additional embodiments also include a controller in communication with multiple optical switching components and configured to drive the piezoelectric actuators of each of the multiple optical switching components. In this way a single controller can orient multiple optical switching components simultaneously.
The present invention also includes a method for switching an optical signal. The method comprises providing an optical switching device of the present invention, receiving an instruction at a controller, applying a voltage to a first piezoelectric actuator to orient a top surface of a rotor such that an angle of incidence is substantially equal to an angle of reflectance, and emitting a beam from an emitter port such that it reflects off the top surface and is received by a receiver port.
The present invention also includes a method for making an optical switching component. The method comprises providing a substrate, forming a stator by defining a cavity within the substrate, forming a mask layer over the stator and filling the cavity, forming an opening in the mask layer, forming within the opening a rotor and a pivotal connection to the stator, removing the mask layer, and forming a piezoelectric actuator between the stator and the rotor.